Stagnation flow length scales

The traditional view of stagnation flow was presented in the previous sections, that is, a semi-infinite inviscid potential flow interacting with a thin viscous boundary layer near the stagnation surface. In that case there is no physically based characteristic length scale. 

As with semi-infinite stagnation flow, there are no natural physically observable length and velocity scales that form the basis for nondimensionalization. Rather, mathematically derived length and velocity scales lead to a nondimensional system of equations that are parameter free. These scales are... 

In the foregoing sections the discussion of axisymmetric stagnation flows has concerned four subcases of the same general problem—semi-infinite or finite domains and rotation or no rotation. The intent of this section is to focus attention on the fact that with suitable choices of length and velocity scales these problems can be collapsed to a common representation. Generally speaking, the length scale is called L and the velocity scale is called U. Thus nondimensional variables are defined as... 

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